Flush patch for elastomeric implant shell

ABSTRACT

An elastomeric prosthetic breast implant is provided having a shell and a patch forming a flush interface with the shell and no sudden surface steps on both interior and exterior surfaces of the shell.

RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.12/431,070, filed Apr. 28, 2009, which claims the benefit of U.S.Provisional Patent Application No. 61/038,919, filed on Apr. 28, 2008,the entire disclosure of which is incorporated herein by this specificreference.

FIELD OF THE INVENTION

The present invention relates to patches for elastomeric implants and,more particularly, to devices and methods for forming a patch flush withan elastomeric implant shell.

BACKGROUND OF THE INVENTION

Implantable prostheses are commonly used to replace or augment bodytissue. In the case of breast cancer, it is sometimes necessary toremove some or all of the mammary gland and surrounding tissue thatcreates a void that can be filled with an implantable prosthesis. Theimplant serves to support surrounding tissue and to maintain theappearance of the body. The restoration of the normal appearance of thebody has an extremely beneficial psychological effect on post-operativepatients, eliminating much of the shock and depression that oftenfollows extensive surgical procedures. Implantable prostheses are alsoused more generally for restoring the normal appearance of soft tissuein various areas of the body, such as the buttocks, chin, calf, etc.

Soft implantable prostheses typically include a relatively thin andquite flexible envelope or shell made of vulcanized (cured) siliconeelastomer. The shell is filled either with a silicone gel or with anormal saline solution. The filling of the shell takes place before orafter the shell is inserted through an incision.

One process for forming flexible implant shells for implantableprostheses and tissue expanders involves dipping a suitably shapedmandrel into a silicone elastomer dispersion. The outer siliconeelastomer shell may have an anatomical configuration, in this casematching the breast, and comes off the mandrel with a shell hole. Apatch over the shell hole typically includes an uncured portion directlyover the hole and a cured portion covering that and adhered to the innersurface of the shell. The patch is cured and then the hollow interior ofthe shell is filled with an appropriate gel via a needle hole in thepatch. The needle hole in the patch is then sealed with a siliconeadhesive and the implant oven cured to achieve cross-linking of the gel.

Another process for forming implant shells is rotational molding, suchas the system and methods described in U.S. Pat. No. 6,602,452 toSchuessler. The process also results in a flexible implant shell havinga hole that requires a patch.

Patches for flexible implant shells are sized larger than themanufacturing hole to provide some bonding area. The overlap of thepatch on the shell results in a slight surface step on the inside oroutside of the shell which may be noticeable in the finished product,which is undesirable. Also, such a palpable step or discontinuity mayirritate tissue in contact with the exterior of the implant.

Despite many advances in the construction of soft prosthetic implantshells, there remains a need for a smoother joint between a patch and amanufacturing hole in the implant shell.

SUMMARY OF THE INVENTION

In accordance with the present invention, a hollow medical implantcomprises an elastomeric hollow shell having a contiguous and consistentwall except in an access region, and a patch extending thereacross. Thepatch is securely bonded to the shell and a peripheral edge of the patchand the shell cooperate to form a flush interface with no surface stepson both interior and exterior surfaces of the implant.

In another aspect, the invention includes a hollow medical implant,comprising an elastomeric hollow shell having a contiguous andconsistent wall except in an access region. A patch extends across theaccess region of the shell and securely affixes thereto. The patch hasan outer flange and the shell wall forms an exterior butt joint againsta peripheral edge of the flange and overlaps an inner surface of theflange in a manner that results in no surface steps.

Both the elastomeric hollow shell and patch may be made of materialswith similar elastic modulus, durometer and elongation, and may even bemade of the same material. Desirably, the elastomeric hollow shell ismade of a solvent-based solid elastomer and the patch is made of aliquid silicone rubber without a solvent. In one embodiment, the patchincludes a stem projecting radially inward into the interior of thehollow shell and an outer flange extending circumferentially outwardfrom the stem, wherein the shell wall forms a flush butt joint against aperipheral edge of the flange and overlaps an inner surface of theflange and extends at least to the stem. In another embodiment, thepatch is a substantially flat disk shape and the shell wall covers anentire inner face of the patch. The patch flange may increase in radialthickness from its periphery toward its center such that the portion ofthe shell wall that overlaps the inner surface of the flange is thickestadjacent the flange periphery.

In one form, the implant is for implantation in the breast and theelastomeric hollow shell is accordingly shaped. Other implantapplications include for the buttocks, testes, calf, etc. In someembodiments, the implant is a tillable implant, for example, a salinetillable breast implant or tissue expander. In other embodiments, theimplant is an intragastric balloon.

In some embodiments, the implant is a tillable or inflatable implantsuch as a saline finable breast implant or an inflatable intragastricballoon and the patch includes a fill valve for facilitating inflationof the implant.

The present invention also embodies a method of formation of a medicalimplant, comprising:

providing a mold cavity having a sprue orifice;

covering the sprue orifice with a patch;

introducing a silicone elastomer into the mold cavity;

causing the silicone elastomer to distribute generally evenly around themold cavity and over at least a portion of the patch;

curing the silicone elastomer to form a hollow implant shell having thepatch bonded thereto; and

removing the implant shell from the mold cavity.

The patch may be shaped relative to and positioned within the moldcavity so that after formation of the hollow implant shell a peripheraledge of the patch and the shell cooperate to form a flush interface withno sudden surface steps on both interior and exterior surfaces of theimplant. The step of introducing preferably includes introducing thesilicone elastomer into the mold cavity through the patch. During thestep of causing the silicone elastomer to distribute generally evenlyaround the mold cavity the method may include extending a vent tubethrough the patch and venting gas from within the mold cavity though thevent tube. Also, a tube may be inserted through the patch for fillingthe mold cavity with a silicone gel through the tube, which is thencured to form a solid prosthesis.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the present invention will become appreciatedas the same become better understood with reference to thespecification, claims, and appended drawings wherein:

FIG. 1 is a plan view from above of a elastomeric implant sealed by apatch construction in accordance with the prior art;

FIG. 2 is a cross-section, to a slightly enlarged scale, when viewed onsection line 2-2 of the FIG. 1;

FIG. 3 shows, in cross-section, an alternative patch construction inaccordance with the prior art with a chamfered edge of the aperture tobe sealed by the patch;

FIG. 4 shows, in cross-section, an alternative patch construction inaccordance with the prior art;

FIG. 5 shows, in cross-section, a still further alternative patchconstruction in accordance with the prior art;

FIG. 6 is a schematic cross-section of an exemplary rotational moldingsystem for use in forming the shell of a soft prosthetic implant of thepresent invention;

FIGS. 7 and 8 are bottom and sectional views of one embodiment of a moldfor use in a rotational molding system such as shown in FIG. 6 to forman elastomeric implant that receives a flush patch of the presentinvention;

FIG. 9 is a cross-sectional view through an exemplary mold of thepresent invention showing various elements of a process for forming aflush patch;

FIG. 10 is a cross-sectional view through an exemplary gel-filled breastimplant prosthesis having a molded-in-place flush patch formed inaccordance with the present invention;

FIG. 11A is a detailed view of the interface between the flush patch andthe shell of the breast implant prosthesis of FIG. 10; and

FIG. 11B is a detailed view of the interface between an alternativeflush patch and the shell of the breast implant prosthesis of FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a gel-filled implant prosthesisincorporating a shell composed partly or entirely of a fluid barrierlayer, preferably a silicone elastomer. The implant shells of thepresent invention may have a single material layer of homogeneous oruniform composition, or a laminated or layered configuration. Theprimary application for gel-filled soft implants is to reconstruct oraugment the female breast. Other potential applications are implants forthe buttocks, testes, or calf, among other areas. Moreover, though thepresent invention is particularly advantageous for gel-filled implants,saline filled breast implants or intragastric balloons may be modifiedto incorporate the benefits herein. Further, tissue expanders which maynot be viewed as implants, per se, may also use the concepts disclosedherein. For that matter, the term implant as used herein refers to longand short-term implanted devices.

The implant shells of the present invention are desirably formed using arotational molding system, such as disclosed in U.S. Pat. No. 6,602,452to Schuessler, which is expressly incorporated herein by reference.Schuessler discloses a rotational molding machine for forming medicalarticles, in particular for molding silicone elastomer shells for breastimplants. Molding machines other than those that rotate the mold, suchas insert molding machines in general (the insert being the patch), mayconceivably be used to mold in place the flush patch as describedherein, and the advantages of the present invention may even beincorporated into traditional dip molding method, though modificationsto the typical dipping mandrel and rod are necessary and will not bedescribed herein.

The advantage of insert molding the patch in place within the shell isthat the patch integrates with the shell. That is, the shell materialflows over and around the patch and bonds tightly thereto, if notactually melding together to blur any distinct boundaries between thetwo items. How much of this integration occurs depends on the similarityin the materials, and the mold process parameters such as time andtemperature. Preferably the shell comprises a solvent-based solidelastomer (e.g., silicone) and the patch is formed of a liquid siliconerubber (LSR) without a solvent and with a similar elastic modulus,durometer and elongation as the shell. Similar physical propertiespermits the patch to deform and stretch with the shell which reducesstress concentrators. Alternatively, the materials of the patch andshell could be identical.

FIGS. 1 and 2 of the drawings illustrate a flexible implant constructionof the prior art. A breast prosthesis 21 comprises a textured envelopeor shell 22 formed by a conventional molding process on a mandrel. Apatch 23 covers an aperture in the shell 22 formed during the moldprocess. As best seen in FIG. 2, the patch 23 comprises an externaloverlay 24 and an internal underlay 25, with respective overlappingportions 26, 27, so as to form a sandwich structure. The overlappingsections of the patch 23 and shell 22 as well as those portions of theoverlay 24 and underlay 25 which are in contact are bonded together.

The patch can be bonded to the shell by a variety of means includingchemical welding or bonding, ultrasonic welding, and heat/pressurefusing. One disadvantage of this process is that a ridge 28 is formed onthe exterior as well as a concentric ring 29 formed by the bondingprocess, part or all of which may be smooth, i.e. where the texturedexterior surface area of the shell 22 may be reduced by the overlap ofthe overlay 24. This is undesirable, because the exterior texturedsurface area ought to be maximized for surgical reasons. Moreover, thecircular ring 29 and peripheral ridge 28 form a ridge on the breastprosthesis 21 that is discernible by feel after implantation. Theperipheral portion 27 of the underlay 25 also presents a small internalridge which is palpable after implantation. These physicaldiscontinuities not only present unnatural tactile sensations, but mayresult in undesirable chafing between the prosthesis 21 and the breastcavity.

FIG. 3 illustrates an implant shell 33 of the prior art having achamfered edge 32 around the mold aperture and opening toward theinterior of the shell. A patch member 34 bonded to the interior of theshell 33 includes a conical portion which fits closely against thechamfered edge 32 and a peripheral skirt 35 that abuts the interior ofthe shell 33. This construction eliminates an external ridge, such as at28 in FIG. 2, but the peripheral skirt 35 still presents an interiorridge.

Alternatively, as shown in FIG. 4, a patch applied from the interior ofthe shell 33 in FIG. 3 may comprise two parts, a cap plug portion 34 a,slightly larger than the aperture, and an underlay portion 34 b, largerstill, such that when bonded together, the whole patch extends radiallyaround the aperture in the same manner illustrated in FIG. 3.

The configurations shown in FIGS. 3 and 4 have the advantage that astronger bond is formed between the edge of the aperture and the patch,since the edge area is increased by virtue of the chamfer 32, whencompared to a squared edge, and that no ridge is formed on the exteriorat the joint between the patch and the shell. However, as mentionedabove, an interior ridge remains. It will be appreciated that thepresence of any detectable seam between the patch and the shellrepresents a stress point which could possibly fail giving rise toleakage of fluid from the prosthesis, which must be avoided.

Finally, FIG. 5 illustrates another patch configuration of the prior artin which a prosthesis 40 includes a patch 42 closing a mold aperture ofa shell 44. The patch 42 comprises an external surface 46 visiblethrough the aperture, and an internal surface 48. The aperture has achamfered mouth 52 to which a peripheral extent of the external surface46 conforms. The internal surface 48 extends outward from the mouth 52in a skirt 54 that terminates at a peripheral edge 56. This patchconfiguration once again presents a smooth external surface to theprosthesis 40, with no ridge, and is somewhat more streamlined thanearlier versions, but the internal peripheral edge 56 remains. Again,the edge 56 presents a relatively sudden surface step and stress pointaround the patch 42 that is discernible from outside the patient afterimplantation. In this context, a surface step is a relatively suddensurface change such as an increase or decrease in thickness at the shellwall/patch boundary.

FIG. 6 is a schematic of an embodiment of a rotational molding systemsimilar to that disclosed in Schuessler, U.S. Pat. No. 6,602,452, whichcan be used to form implant shells of the present invention. A two-piececase mold 120 affixes to a multi-axis rotational mold machine 122 byclamps securing top mold piece 124 and bottom mold piece 126 to clampbase 128 at top locking groove 130 and bottom locking groove 132,respectively. Vacuum connection 134 runs through one arm of the moldmachine 122 to a vacuum opening 135. Material connection tube 136,through which silicone elastomer, liner materials, and/or air areinjected into the mold cavity 140, may run through or along the same arm142 as the vacuum connection 134 or by means of another arm 144. Theinput fluid then continues through a circular sprue tube 145 fitted in acircular opening (not numbered) of bottom mold piece 126. The sprue tube145 defines a hollow bore that allows materials to enter an internalcavity of the two-piece case mold 120.

The hub 146 of the two arms rotates about axis A in the horizontaldirection, while the arms 142, 144 rotate about axis B, which may beperpendicular to axis A. This allows a liner material or siliconeelastomer material to uniformly coat the surface of the mold cavity 140.Two-piece case mold 120 may be manufactured from copper, aluminum, orother materials. The top mold piece 124 and bottom mold piece 126 fittogether at their mating surfaces, seal with an O-ring 150, and thenlock into clamp base 128 of multi-axis rotational molding machine 122.

Material reservoir 152 is fluidly coupled to connection tube 136 forproviding silicone elastomer, liner material and/or air to cavity 140.Vacuum source 154 and solvent condenser 156 are fluidly coupled tovacuum connection 134. The hollow bore of the sprue tube 145communicates with an inner vacuum tube (not shown) which in turn isconnected to vacuum opening 135 and vacuum connection 134.

The rotational molding system of FIG. 6 has two distinct advantages overearlier methods for forming soft implant shells. First, the systemincludes a vacuum vent to the mold via a rotating arm of the equipment,which removes the solvent from silicones and other solvent-based orgas-emitting materials. A second advantage of the rotational moldingsystem is that it enables the formation of articles without seams at themold parting lines by first coating the inside of the mold with a thinlayer of molding material such as polyethylene, polypropylene, nylon,fluoropolymer, polyester resin, polyurethane, epoxy or the like tocreate a mold liner. After the liner is cast, then the raw material,e.g. silicone elastomer, for the desired implant shell is injected intothe mold cavity and similarly rotationally cast inside the liner,resulting in a temporary laminated construct. When the mold isdisassembled and the construct is removed from the mold, the linermaterial and the implant are physically separated resulting in thedesired article having a seamless configuration.

FIGS. 7 and 8 illustrate an alternative mold 200 for a rotationalmolding system, such as that described with reference to FIG. 6, whichcan be used to form implant shells of the present invention. As in theearlier embodiment, the mold 200 comprises a top mold piece 202 andbottom mold piece 204 held together by bolts 206 across respectiveflanges 208. An inner liner 210 is illustrated in cross-section in FIG.8. Again, the presence of the inner liner 210 is a significant advantagebecause the implant shells may be formed without a seam that otherwisewould result at the intersection of the two mold pieces 202, 204.Desirably, the mold pieces 202, 204 are formed of a metal such asaluminum, and the inner liner 210 is formed of a non-adherent materialsuch as Teflon, for instance ETFE (ethylene-tetrafluoroethylene).

In contrast to the earlier-described embodiment, the inner liner 210 isintended to be reused every time a prosthetic implant shell is formed bythe mold. The inner liner 210 remains within the cavity formed by themold pieces 202, 204, and thus defines the inner surface of the mold200, during the formation of a number of implants. Preferably the innerliner 210 may remain within the mold pieces 202, 204 for hundreds ofuses. As with the earlier-described embodiment, the inner liner 210 isinitially formed by rotational molding by injecting free-flowing linermaterial within the mold pieces 202, 204. The mold 200 functions muchlike the aforementioned two-piece case mold 120, in that it includes arelatively large circular opening 212 within a lower flange 214 throughor into which inserts a sprue tube (such as the sprue tube 145 of FIG.6).

FIG. 9 schematically illustrates an alternative single-piece mold 220mounted on a rotational molding machine, such as described above, in theprocess of forming a soft implant 240 comprising an implant shell 244having a molded-in patch 242, seen finished in FIG. 10. A single-piecemold 220 obviously eliminates any seam between mold parts, and thus amold liner is unnecessary. After the implant shell 244 with the moldedin-patch 242 is formed, the mold 220 is disengaged from the rotationalmolding machine leaving the patch visible through a mold neck 222. Theresiliency of the material used for the patch and the shell enables themto be folded or otherwise compressed then removed from the mold neck222.

The molding process involves introducing a silicone dispersion withinthe mold cavity, rotating the mold 220, and permitting a solvent withinthe silicone dispersion, such as xylene gas, to be evacuated through avent tube that extends centrally through the patch 242. The siliconedispersion may be introduced straight into the mold through the patchwhile holding the patch 242 in place, such as with a spring (not shown),or another channel may be used for inserting the silicone. A mold plugcontacts an external surface of the patch 242 and seals within the moldneck 222. The vent tube passes through a bore in the mold plug, and fromthere to a vacuum and solvent collection system.

FIG. 10 is a cross-sectional view through the exemplary gel-filledbreast implant prosthesis 240 comprising the shell 244 andmolded-in-place patch 242. The prosthesis 240 may be filled with a gel246, such as silicone gel.

The patch 242 provides a reinforced access region on the surface of theprosthesis 240 for passage of one or more implements from the exteriorto the interior. For instance, the mold process described abovedesirably utilizes the patch 242 as a reinforced conduit through whichboth the silicone dispersion tube inserts, as well as the vent tube asshown in FIG. 9. Subsequent to the shell molding process, a third tubemay be inserted through the patch to fill the interior of the shell witha silicone gel. And of course a primary function of the patch 242, asdetailed herein, is to enable formation of a totally seamless implantwith no surface steps inside or out.

FIG. 11A is a detailed view of the interface between the patch 242 andthe shell 244. The patch 242 includes a stern 250 projecting directlyradially into the interior of the shell 244 and an outward flange 252generally conforming to and forming a continuation of the exterior shapeof the shell 244. The material of the shell 244 extends over theinternal surface of the flange 252 at ring 260, extending at least tothe stern 250, and preferably continues in a tube 262 around the stern250. Because the patch flange 252 increases in radial thickness from itsperiphery toward its center, the wall thickness of the ring 260 tapersthinner from the main part of the shell 244 to the tube 262, andpreferably has a uniform thickness along the stern 250. By virtue of theimplant material extending therearound, the patch 242 is securely heldin place.

By introducing the patch 242 during the process of molding the shell244, rather than applying the patch to the shell aperture afterwards,the patch integrates with the casting material flowing over and around,thus producing a flush surface both inside and out. In particular, anexternal surface of the prosthesis including a circular interface line270 at a flush butt joint between the patch 242 and shell 244 has noridges or other surface irregularities. A butt joint means thejuxtaposition of two edges, in this case an inner-facing edge of theshell 244 and the peripheral edge of the patch 242. The absence ofsurface interruptions is a great advantage in reducing irritation totissue surrounding the implanted prosthesis, which has been traumatizedand is susceptible to inflammation. Likewise, an internal surface of theprosthesis in the area of the patch 242 has no surface irregularities,and in particular the boundary between the patch 242 and shell 244 isrelocated to the radially inner end 272 of the stem 250. Furthermore,molding the patch 242 into the shell 244 eliminates a secondarymanufacturing step of adhering a patch to the shell.

It is important to note that while prior implants utilized a patch tocover an aperture left over as an artifact of the mold process, theshell 244 actually has no such aperture. More accurately, the shell 244has a contiguous and consistent wall except in an access region acrosswhich the patch 242 extends. That is, the access region interrupts thegenerally constant thickness shell wall. The patch 242 provides anaccess medium or port through which tubes or other instruments may beinserted into the inner cavity of the shell 244. In the access region,the material of the shell thins to form the ring 260 over the internalsurface of the flange 252 and the tube 262 around the stem 250. Becausethe material of the shell 244 does not cover the open top of the stem250, an aperture through the shell technically exists, though not thesame type of aperture as previously seen with prior art shells. Indeed,in an alternative version in FIG. 11B the shell may not even have anaperture, and the patch in that case does not cover anything but ratherparallels, supports, or is juxtaposed against the thinned access regionto provide the access port. In this sense, therefore, the term “patch”is sort of a misnomer, but will be retained for the sake of familiarity.

The stem 250 of the patch 242 may be utilized to help prevent cloggingof tubes inserted into the cavity of the mold. For example, as seen inFIG. 9, a vent tube extends through a channel 274 (FIG. 11A) in thepatch 242 and extends into the mold cavity through the inner end 272 ofthe stem 250. The silicone dispersion that may at times aggregate nearthe patch 242 is prevented from entering and potentially clogging thevent tube by virtue of imposition of the upstanding stem 250. Thechannel 274 also provides an avenue through which a gel-filling tube(not shown) may be introduced after the shell 244 and patch 242 aremolded together. For instance, a gel, such as silicone gel 246 shown inFIG. 10, may be injected through a tube inserted through the channel274. Therefore, the channel 274 may be used for introducing silicone tothe mold to form the shell, for venting the mold cavity during the moldprocess, and/or for introducing the silicone gel into the hollowprosthesis. Instead of providing a pre-formed channel 274, the patch 242may be made of a material or be configured to be self-sealing. However,given the relatively large bore tubes that may pass through the patch, achannel that is subsequently sealed is more practical. A small well atthe opening of the channel 274 that helps guide the vent and gel filltubes into the channel may be filled with a silicone plug 276, such as asilicone adhesive, to form a completely even outer prosthesis surface.

FIG. 11B illustrates a portion of a soft implant prosthesis 240′ thatincorporates a low-profile flush patch 242′. The patch 242′ includes anoutwardly extending flange 252′ but differs from the above-describedpatch 242 by eliminating the radially extending stem, and instead has asubstantially flat disk shape. The patch 242′ molds in place so that thesurrounding shell 244′ again meets flush in a butt joint with theoutward flange 252′ to form a smooth exterior surface interface 270′.The material of the shell 244′ also flows over the inner face of thepatch 242′ to form a cap 260′ that completely eliminates any internalboundary between the patch and shell. The region 272′ of the shell 244′adjacent and inward with respect to the outer edge of the patch flange252′ is smooth, and the thickness of the shell 244′ at that pointentirely covers and cushions any potential tactile discontinuitypresented by the edge of the flange. There are certainly no suddensurface steps inside and outside the patch periphery, as in the priorart. A self-closing channel 274′ through the patch 242′ again providespassage for insertion of a vent or gel fill tube, and a small plug 276′fills a small well at the outlet of the channel after formation of theimplant 240′.

It is contemplated by the inventors that a fill valve can be provided inthe patch for facilitating inflation and deflation of the implant shell.For example, the implant may be an intragastric balloon and the patchmay include a valve useful for both inflating and deflating the balloon.In other embodiments of the invention, the implant may be a salinefillable breast implant or a tissue expander and the patch may include asuitable valve for enabling filling and or draining of the implant. Allof these are considered to fall within the scope of the presentinvention.

For breast implants, the formed shell is ready for further assembly orprocessing consistent with the usual manner in creating a final breastimplant product. For example, the implant shell is filled with a fillermaterial of silicone gel or other biocompatible gel material well knownto those of skill in the art, such as gel 246 shown in FIG. 10.

Although the invention has been described and illustrated with a certaindegree of particularity, it is understood that the present disclosurehas been made only by way of example, and that numerous changes in thecombination and arrangement of parts can be resorted to by those skilledin the art without departing from the scope of the invention, ashereinafter claimed.

1. A method of formation of a medical implant, comprising: providing amold cavity having a sprue orifice; covering the sprue orifice with apatch; introducing a silicone elastomer into the mold cavity; causingthe silicone elastomer to distribute generally evenly around the moldcavity and over at least a portion of the patch; curing the siliconeelastomer to form a hollow implant shell having the patch bondedthereto; and removing the implant shell from the mold cavity.
 2. Themethod of claim 1, wherein the patch is shaped relative to andpositioned within the mold cavity so that after formation of the hollowimplant shell a peripheral edge of the patch and the shell cooperate toform a flush interface with no sudden surface steps on both interior andexterior surfaces of the implant.
 3. The method of claim 1, wherein thestep of introducing includes introducing the silicone elastomer into themold cavity through the patch.
 4. The method of claim 1, wherein duringthe step of causing the silicone elastomer to distribute generallyevenly around the mold cavity the method further includes extending avent tube through the patch and venting gas from within the mold cavitythough the vent tube.